As technologies further advance, wireless power transfer has emerged as an efficient and convenient mechanism for powering or charging battery based mobile devices such as mobile phones, tablet PCs, digital cameras, MP3 players and/or the like. A wireless power transfer system typically comprises a primary side transmitter and a secondary side receiver. The primary side transmitter is magnetically coupled to the secondary side receiver through a magnetic coupling. The magnetic coupling may be implemented as a loosely coupled transformer having a primary side coil formed in the primary side transmitter and a secondary side coil formed in the secondary side receiver.
The primary side transmitter may comprise a power conversion unit such as a primary side of a power converter. The power conversion unit is coupled to a power source and is capable of converting electrical power to wireless power signals. The secondary side receiver is able to receive the wireless power signals through the loosely coupled transformer and convert the received wireless power signals to electrical power suitable for a load.
As power consumption has become more important, there may be a need for accurately monitoring the current flowing through the transmitter of the wireless power transfer system so as to achieve a high-efficiency, safe and reliable wireless power transfer between the transmitter and the receiver. Current sense devices such as current sense resistors have become the preferred choice for achieving high performance (e.g., accurate current measurement information) because current sense resistors can be connected in series with one power switch of the transmitter. However, as the current flowing through the power switch of the transmitter goes higher, the power loss of the current sense resistors has become a significant issue, which presents challenges to designers of wireless power transfer systems.
It would be desirable to have a current sense apparatus for use in high power wireless power transfer applications exhibiting good behaviors such as highly-accurate current sensing and low power consumption. It would be also necessary to achieve the reliable foreign object detection (FOD) in the wireless power transfer applications by using highly-accurate current sensing.